The invention relates to a device for adapting the actual tire pressure of at least one tire of a wheel of an axle of a vehicle to a current setpoint tire pressure during travel.
Vehicles which are used under significantly different road conditions, such as metalled roads, off-road, sandy or marshy conditions, require the tire pressure to be adapted to the different operating conditions even during travel.
DE 38 36 105 A1 discloses a device for adapting the actual tire pressure of at least one tire of a wheel of an axle of a vehicle to a current setpoint tire pressure during travel, in which device a pressure control apparatus, which rotates with the wheels, is coupled by means of two lines to a chassis-side central controller. One line serves to inflate and vent the tires and the other line to control the wheel control units. For this reason, two rotational connections are also necessary between the chassis-side, rotationally fixed line parts and line parts which rotate with the wheel, which leads to high costs and to a low level of reliability because the rotational connections mentioned above are prone to leaks.
Furthermore, DE 3 836 105 A1 and DE 3 246 601 A1 each disclose a device for adapting the actual tire pressure to a current setpoint tire pressure during travel with just one line, where the individual line serves both for performing control and for inflating and venting the tires. Pressure pulses are necessary to open and/or close a wheel-side control valve apparatus, as a result of which the chassis-side central apparatuses are relatively complex. According to DE 2 630 511 A1 and DE 3 300 457 A1, the chassis-side central apparatuses are electronically controlled for this purpose, wherein such an electronic controller can be critical with respect to its reliability, in particular under extreme operating conditions which off-road vehicles are in fact subjected to.
DE 10 360 764 A1 discloses a device for adapting the actual tire pressure to a current setpoint tire pressure during travel, in which in order to vent the tires the compressed air is conducted into the open air through a venting opening of the wheel-side pressure control apparatus. This solution is disadvantageous because of the possible soiling of the venting opening, in particular when travelling through water or in the case of amphibious vehicles.
For example, DE 2 929 894 A1 discloses a solution in which overflow valves are used as 2/2-way valves that are spring-loaded into the closed position and loaded into the open position by the setpoint tire pressure in the wheel-side pressure control apparatus. This has the disadvantage that these valves open and close only within a relatively small pressure range (pmax/pmin approximately 4:1), and only small through-flow cross sections are available during the venting of the tire at small pressure values, as a result of which the time period of the venting is very long.
EP 0 368 365 A1 discloses a solution in which the wheel-side pressure control apparatus is designed according to the principle of an overflow valve which is actuated pneumatically. However, the pneumatic actuation is intended to prevent the tire continuing to be inflated, and the compressed air container emptied, when the tire is damaged.
In DE 31 08 247 A1, an overflow valve, which is actuated pneumatically, is also used in the wheel-side pressure control apparatus. In this context, a ram pressure or differential pressure, which originates from a throttle formed in the supply line, is used as the control pressure. This principle has the disadvantage that in the case of low throttling, in order to avoid delaying the inflation and venting, the pressure range is also only relatively small, or in the case of more effective throttling the inflation and venting time is relatively long.
DE 2 823 045 A1 discloses a solution in which the inflation and venting are carried out by a pilot-controlled wheel control valve. Owing to the pilot control, rapid closing of the wheel control valve can take place, but only if the maximum permitted tire pressure is reached. When the tire pressures to be set are lower than the maximum permitted tire pressure, and in particular in the case of a reduction in the tire pressure, the pilot control is not active, with the result that the wheel control valve does not close until the minimum pressure occurs, wherein the closing pressure is defined by spring forces of spring device and is constant. In contrast, at pressures between the maximum and the minimum tire pressure, the wheel control valve remains open, as a result of which the lines and rotational connections are not pressure-relieved, which reduces the reliability.
The invention is accordingly based on the object of developing a device for adapting the actual tire pressure of at least one tire of a vehicle to a current setpoint tire pressure during travel in such a way that the device permits rapid adaptation of the pressure with a high level of reliability and a simple design.
This and other objects are achieved according to the invention by providing a device for adapting the actual tire pressure of at least one tire of a wheel of an axle of a vehicle to a current setpoint tire pressure during travel, comprising:
a) a chassis-side central apparatus which either feeds the current setpoint tire pressure into a connection, which rotates with the wheel, of an axle- or wheel-related pneumatic pressure control apparatus in order to adapt the actual tire pressure to the setpoint tire pressure, or vents this connection if the actual tire pressure is equal to the setpoint tire pressure, wherein the pressure control apparatus contains at least one further connection to which the actual tire pressure can be applied,
b) at least one control valve having an open position which connects the one connection to the other connection and having a closed position which closes this connection, wherein the control valve is controlled pneumatically in opposite directions, and one of its pneumatic control connections is connected to the one connection,
c) the pressure control apparatus contains at least one pilot control valve which performs pilot control of the control valve and which feeds either the pressure present at the one connection or the actual tire pressure present at the other connection into the other pneumatic control connection of the control valve or prevents such feeding in,
d) the pilot control valve is controlled pneumatically at least by a pressure present at the one connection and/or at least by the actual tire pressure present at the other connection, and
e) the pressure control apparatus has a bypass line which bypasses the control valve and the pilot control valve and connects the one connection to the other connection and has a nonreturn valve which opens in the inflation direction of the tire and closes in the venting direction of the tire.
The advantage of these measures is that, on the one hand, only a single line between the central apparatus and the pressure control apparatus, and therefore also only a single rotational connection per wheel, is necessary between the rotationally fixed line part and the rotating line part for the control and also for the inflation and venting. This has a favorable effect on the reliability of the device because the seal of such a rotational connection wears more quickly under pressure.
Overall, the rotational connection of the single line extending between the rotationally fixed line part and the rotating line part between the central apparatus and the pressure control apparatus is loaded merely in phases of the adaptation of the actual tire pressure to the setpoint tire pressure and is otherwise relieved of pressure, as a result of which the seal of the rotational connection is loaded only briefly.
With the device according to the invention, in order to adapt the actual tire pressure to a new setpoint tire pressure, all that is necessary is to load the one connection with the new setpoint tire pressure to be set, which permits a simple, cost-effective and reliable central apparatus.
Furthermore, the venting in order to reduce the actual tire pressure takes place via the line between the wheel-side or axle-side pressure control apparatus and the central apparatus on the chassis side, for which reason problems with the ingress of dirt or moisture in the case of venting through the wheel-side or axle-side pressure control apparatus are avoided.
With the solution presented here, the control valve of the pressure control apparatus serves preferably to adapt the tire pressure in a pressure range which is below a predefined pressure threshold value, wherein this pressure range is extended upward, that is to say for pressures higher than this threshold value, by virtue of the fact that the control valve is pilot-controlled by the pilot control valve.
The control valve is particularly preferably a pneumatic 2/2-way valve. The pilot control valve is likewise preferably a pneumatically controlled 2/2-way valve which has a closed position and an open position and which, in the open position, feeds either the pressure present at the one connection or the actual tire pressure present at the other connection into the other pneumatic control connection of the control valve and in its closed position prevents such feeding in.
According to one preferred embodiment, the pilot control valve can be loaded into the closed position by a spring device, which spring device is configured in such a way that the pilot control valve is held in the closed position for pressure values of the pressure at the one connection which are lower than an upper threshold value, and is switched to the open position for pressure values of the pressure at the one connection which are higher than or equal to the upper threshold value.
In this case, the control valve interacts with the pilot control valve in such a way that:
a) the control valve is switched to the open position and the pilot control valve is switched to the closed position for pressure values of the pressure present at the one connection which are lower than the upper threshold value, and
b) the control valve is switched to the closed position and the pilot control valve is switched to the open position for pressure values of the pressure present at the one connection which are higher than or equal to the upper threshold value.
With these measures, a relatively high pressure setting range can be achieved for the setpoint tire pressure.
According to one alternative embodiment, the pilot control valve is a pneumatically controlled difference pressure valve which is loaded into the open position by the pressure present at the one connection and loaded into the closed position by the actual tire pressure present at the other connection. In this context, the pilot control valve can additionally comprise a spring device which prestresses it into the open position, wherein the pilot control valve is switched to the open position for pressure values of the pressure at the one connection which are higher than or equal to the actual tire pressure present at the further connection, and is switched to the closed position for pressure values of the pressure at the one connection which are lower than the actual tire pressure present at the further connection. As a result, a relatively high pressure setting range can also be achieved for the setpoint tire pressure which is present at the one connection.
As already indicated above, the one connection preferably constitutes a single connection for connecting the pressure control apparatus to the chassis-side central apparatus. The respective setpoint pressure is therefore fed into the pressure control apparatus via the single line between the chassis-side central apparatus and the wheel-related pressure control apparatus, a single rotational connection and a single chassis-side connection, which setpoint pressure at the same time forms the supply pressure for the respective tire and the control pressure for the pressure control apparatus.
The chassis-side central apparatus is therefore connected to the pressure control apparatus via a line which has an axle-side, rotationally fixed line part and a line part which rotates with the wheel, and a rotational connection between the rotationally fixed line part and the line part which rotates with the wheel.
According to one development, at least one pneumatic safety valve is connected, as a 2/2-way valve, between the control valve and the further connection, which pneumatic safety valve is loaded at its pneumatic control connection into the open position by the actual tire pressure present at the other connection, and is switched in a spring-loaded fashion to the closed position in the case of an actual tire pressure below a lower threshold value. In the event of a leak in the tire, further inflation of the tire can be prevented using such a safety valve by virtue of the fact that the actual tire pressure at the other connection then drops and the safety valve controlled by the actual tire pressure switches in a spring-loaded fashion to the closed position in order to decouple the damaged tire from the pressure control apparatus.
The pressure control apparatus preferably has an inflation connection for external application of pressure, this being arranged downstream of the control valve and the other connection in the inflation direction of the tire, so that the tire can be inflated by an external pressure source, for example if the actual tire pressure is below a minimum pressure value such as, for example, after the tire is fitted.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.